Polysilicon resistors are an important component in integrated circuits. It may be desirable to control a doping density in the polysilicon resistor. In replacement gate metal integrated circuits typically transistors with polysilicon gates are first formed and covered with a layer of dielectric. The dielectric layer is then thinned until the tops of the polysilicon gates are exposed. The polysilicon gates are then removed and replaced with metal gates.
Typically when polysilicon resistors are required in these integrated circuits, a thin layer of blocking dielectric is deposited after the dielectric layer is thinned and then patterned and etched to leave dielectric over the polysilicon resistors. The blocking dielectric layer prevents the polysilicon in the resistors from being removed when the polysilicon gates are removed. One disadvantage with forming polysilicon resistors by this method is that the polysilicon resistor height is determined by the thinning process, which may vary from resistor to resistor, across a wafer and between wafers and between fabrication lots. Variation in the height of the polysilicon undesirably results in variation in resistance of the polysilicon resistors.